1. Field of the Invention
The invention relates to antistatic additives for textile fibers, particularly for polyamide fibers, which have reduced flammability as compared to prior art antistatic additives.
2. Description of the Prior Art
It is known to obtain decreased buildup of static electricity charge induced by friction on the surface of synthetic textile materials by the incorporation of antistatic additives at the melt-spinning stage of synthetic fiber production. Water-soluble antistatic additives are disclosed in U.S. Pat. No. 3,475,898 which are the poly(alkylene ether) type polymer. Nylon fibers are improved by the incorporation of said water-soluble polymers which, upon the scouring of textile fabrics made using the modified polyamide fibers so treated, are at least partially removed so as to leave voids in the polyamide polymer which remain where the polyether has been removed.
Antistatic polyamide fibers have also been disclosed in U.S. Pat. No. 3,657,386 and U.S. Pat. No. 3,794,631 in which the antistatic additive is based upon a high molecular weight propylene oxide ethylene oxide copolymer based upon ethylenediamine, either alone or containing as an additional component a fatty acid salt.
Both of the above types of antistatic additives have the disadvantage of being more highly flammable than the polyamide fiber itself and, therefore, the incorporation of such antistatic additives increases the flammability of a nylon fiber. Such undesirable increases in flammability of such antistatic polyamide fibers have been a disadvantage which threatens the continued use of such antistatic additives. It is therefore an object of this invention to provide an antistatic additive which does not contribute to the flammability of a polyamide fiber and, therefore, can be used in a sufficient amount to provide maximum antistatic properties without, at the same time, conferring upon the polyamide fiber increased flammability.
The invention has particular application in the manufacture of a carpet, the face of which is made from fibrous textile material which in use normally tends to accumulate a charge of static electricity.
It is known to impart flame retardancy to a synthetic material by incorporating a flame-retarding agent whereby the flame-retarding agent is made an integral part of the chemical structure of the synthetic material. In U.S. Pat. No. 3,883,611 there is disclosed the use of dibromopentaerythritol incorporated into the chemical structure of a polyester to impart flame retardancy. A block copolyester of poly(ethylene terephthalate/tetramethylene dibromoterephthalate) is disclosed as a means of providing flame retardancy to poly(ethylene terephthalate) which overcomes the undesirable thermally unstable characteristics of such compounds as dibromopentaerythritol.
Recently, a polyester prepolymer of a brominated diol has been disclosed which is prepared by the ethoxylation of 4,4'-isopropylidine(2,6-dibromophenol), commonly referred to as tetrabromobisphenol A. Such prepolymers are disclosed in U.S. Pat. No. 3,794,617 and are said to be particularly useful reactive intermediates for the preparation of fiber-forming copolyesters since the prepolymers of the brominated diol have excellent heat stability and thus show little or no discoloration upon exposure to the high temperatures utilized in the preparation and melt-spinning of polyester fibers. In U.S. Pat. No. 3,909,482 there is also disclosed a process for the production of flame-retardant polyester filaments based upon similar halogenated compounds.
The simplest means of incorporating a flame-retardant chemical to provide resistance to burning has been by a surface treatment of the dyed fabric with one or more flame-retardant additives. Surface treatment of the fabric usually has only a temporary effect and the flame-retardant additive is rapidly lost when the fabric is laundered or drycleaned. As discussed above, relatively permanent flame-retardant effects have been obtained by copolymerizing the halogenated flame-retardant monomers of U.S. Pat. No. 3,883,611 into the polymer structure to obtain reduced burning characteristics or physically mixing such halogenated additives into the polymer. The physical mixtures often detract from the physical properties of the base polymer so that while the flame-retardant effect may be relatively permanent, the fibers may be more brittle or have lower tensile strength or less resistance to oxidative degradation or show reduced color stability.
Halogenated additives which have been incorporated into polymeric materials to render them flame-retardant can include either chlorinated or brominated compounds. It is recognized that brominated compounds are often more effective flame retardants than the corresponding chlorinated materials and that synergistic improvements can be obtained by admixture therewith of certain compounds such as antimony oxide. However, brominated materials have often been limited to applications not involving the use of high temperatures since brominated materials tend to decompose and impart undesirable discoloration to the compositions to which they have been incorporated. With many known brominated compounds having hydroxyl or carboxyl groups the objectionable discoloration is so pronounced at polymerization temperatures that the physical properties of the polymer are adversely affected. Such considerations are important in a flame-retardant antistatic additive which is to be incorporated, for instance, into the polyamide fiber by admixture into the polyamide melt prior to the spinning operation.